Heat spreaders are commonly used in the integrated circuit (“IC”) packaging/assembly industry to dissipate heat generated by high power (for example, >100 W) ICs (ICs are also referred to as chips). Typically, a heat spreader is attached to a back of a chip or an IC package using different types of thermally conductive materials. Such thermally conductive materials are typically provided in a sheet form that has thin adhesive layers on both sides of a pad—the adhesive layers are used to bond the pad (on a first side) to a heat spreader and (on a second side) to a chip or IC package.
The prior art discloses thermally, and non-thermally, conductive elastomeric posts being used in IC packaging applications. In such applications, to create an IC package: (a) posts are formed on a surface of a flexible or a rigid substrate interposer such as a printed circuit board; (b) the posts are then permanently bonded to a chip; (c) the chip is then electrically interconnected to the interposer using standard wire bonding or other interconnect methods; and (d) a dielectric material is then dispensed or injected between the posts to fill voids between the posts.
The prior art also discloses the use of a thermally conductive material, in sheet form, having a series of groves or channels on a first and/or a second surface, which groves or channels are created, for example, by embossing. The groves or channels are disclosed to provide a means for removing air during a bonding process wherein a chip is bonded to the first surface of the thermally conductive material, and a heat sink or a heat spreader is bonded to the second surface.
Thermally conductive pads disclosed in the prior art typically comprise a low modulus material, for example, silicone, that is soft and compliant but which is relatively incompressible—as indicated by a Poisson's ratio of 0.49-0.50. As a result, such thermally conductive silicone pads, with or without embossing, require a high pressure (for example, a pressure between 40 and 50 psi) to bring a heat source and a heat dissipater into intimate contact over a full area of their interface. Such a high pressure is required to distort the silicone pad laterally by an amount sufficient to fill voids at interfaces between: (a) the pad and a surface of the heat source; and (b) the pad and a surface of the heat dissipater. In addition to the use of high pressure to provide intimate contact, the thickness of the low modulus material must be relatively large to enable it to distort laterally to fill voids at the interfaces. However, a large pad thickness is problematic to providing good thermal conductivity. In addition, a problem exists whenever prior art thermally conductive silicone pads are used in device testing applications calling for releasable thermal contactors because prior art contactors have been known to leave residues after high temperature operation of chips.
In light of the above, there is a need in the art for method and apparatus that solves one or more of the above-identified problems.